How to Add a Custom Network to MetaMask
Some Layer 2 chains, testnets, and private networks are not in MetaMask's default list. You can add them yourself using the details each network publishes, as long as you verify those details first.
When you need a custom network
Many EVM-compatible chains are not preloaded. Developers also add local nodes and test networks. Adding a network does not move any funds, but it does let you interact with a chain that may be unfamiliar.
Add it manually
Open the network menu, choose Add a custom network, and enter the network name, RPC URL, chain ID, currency symbol, and block explorer URL. Copy each value from the network's official documentation rather than from a third-party post.
Verify the chain ID
A wrong chain ID or RPC URL can point you at a fake network. Compare both values against an official source, check the currency symbol and explorer link, and only then save the network.